IRF640 and IRF9640 are common MOSFETs and are available at Mouser and many other suppliers. They come in a variety of package styles, so make sure you are selecting the package you need - I think yours would be using TO220. They are in stock for 88 cents and $1.30 respectively.

Try removing the bad transistors then rechecking those diodes. SInce they are in parallel with the transistors, a shorted transistor will make the diode look shorted even when it is not. I have never seen one of those diodes shorted in these units.

THANKS,ENZO
IN THIS DAY AND AGE IT IS NICE TO KNOW THAT THERE
ARE PEOPLE LIKE YOU, WHO ARE CONCERNED FOR OTHERS.
I HAD ALREADY ORDERED THE IRF640 AND THE IRF9640.
BUT I WAS HAVING TROUBLE WITH THE PART NUMBER.FOR THE
DUAL DIODE.
THANKS AGAIN AND IF I CAN HELP YOU WITH ANYTHING ,
JUST LET ME KNOW.
I SORT OF LIKE THIS LITTLE NET (FORUM) I THOUGHT THAT
I WAS THE ONLY ONE HAVING PROBLEMS GETTING SCHM. AND
PARTS FOR THESE NEW AMPS AND MIXERS THAT ARE COMING OUT.

Stan, Behringer in particular is a very uptight company. I am one of their service centers, and we all have to sign a non-disclosure agreement stating that we will not share any of their technical documentation. That is why it is hard to find their schematics. We are free to answer questions such as yours though.

HAve you removed the old shorted IRF640s and checked the diodes? They really are not under any stress, even if the transistors short.